Band brake



Feb. 20, 1951 I Gk WILSON ETAL BAND BRAKE Filed Feb. 26, 1947 Inventors.d. NC L50 Z7 A. .JSZ'LLZeJ Patented Feb. 20, 1951 BAND BRAKE AndrewGordon Wilson and Albert A. Miller, Coventry, England, assignors toSelf-Changing Gear Company Limited, Coventry, England ApplicationFebruary 26, 1947, Serial No. 730,918 In Great Britain September 28,1945 8 Claims. 1

This invention relates to band brakes of the type comprising a brakedrum lapped by at least three gapped brake bands disposed side by side,and wherein the brake operating force is applied to one end of one ofthe bands (hereinafter called the primary band) and the reaction endthereof being coupled to the application ends of the other bands(referred to hereinafter as secondary bands). 7

The object of the invention is to provide, in a band brake of the typedescribed, a balanced brake wherein reaction forces are prevented fromacting transversely of the break drum axis.

The invention consists in a band brake of the type indicated,characterized in this that the reaction ends of the secondary bands areeach connected to means transmitting the reaction equally and in thesame sense to said bands at the opposite side of the axis of the brakedrum in such a manner that the moments of the forces acting about thedrum axis on the application of the brake are substantially balanced.

The invention also consists in a band brake as set forth in thepreceding paragraphs, wherein the balancing means comprise oppositelydisposed equalizing levers interconnected at their inner ends andcarrying at their outer ends re-- spectively reaction and balancinglinks, the said links being preferably also each connected to its leverthrough a slip-friction grip which may be located on the side of thelever fulcrum remote from the link coupling.

The invention further includes a band brake according to the precedingparagraph wherein the force application end of the primary band isconnected by a tie link to a pivoted lever which is located on the sameside of the drum as that on which the reaction link is situated and towhich the braking force is applied.

An alternative means of brake actuation according to the invention andwith the same objects in view, comprises a rod preferably operated by apiston actuated by hydraulic or fluid pressure acting on the fulcrum ofone of a pair of equalizing levers disposed on the side of the brakeband remote from those already referred to, the outer ends of theequalizing levers being connected through links to the primary band onopposite sides of the drum axis, the lever engaged by the rod being freefrom connection with the frame or casing while the other equalizinglever is fulcrummed to the casing, the inner ends of the levers beinglinked or otherwise connected together in the same manner as in the caseof the equalizing levers originally referred to,

Referring to the accompanying drawings:

Figure 1 is an elevation partly in section of a brake constructed inaccordance with the invention;

Figure 2 is an end View of the brake mechanism taken from inside thecasing in the direction of the arrows 2-2 in Figure 1;

Figure 3 is a section of the guide plate for the brake bands taken onthe line 3-3 in Figure 1.

In carrying the invention into effect according to one mode, describedby way of example, a brake drum l which normally rotates in acounterclockwise direction casing 2 having a cover 3 as shown inFigure 1. The drum is encircled by three gapped or circumferentiallydivided brake bands lined with any usual frictional material anddisposed in side by side relationship, with the band gaps all lying tothe left-hand side of the vertical diametric plane of the drum as viewedin Figure 1'. The primary band 4 to which the braking force is appliedis located intermediate the secondary bands 5 and 6 and has secured toone end thereof a pair of hook members 1 to which the braking force isapplied. The opposite (reaction) end of the primary band 4 is secured tothe two adjacent ends of the secondary bands 5 and 6 in any convenientmanner but in the present'instance the primary and secondary bands areintegral, that is to say they are formed by cutting from the same pieceof material, the common portion representing the join between the twobands being indicated at 8. The gap in the primary band is shown at 9and the gaps in the secondary bands at 10 Fig. 2.

The reaction ends of the secondary bands are each provided with a pairof spaced hook lugs l I and Ila, and similarly spaced eye lugs 12 aresecured to the secondary bands in symmetrical relation on the oppositeside of the vertical centre line of the drum.

The balancing mechanism is disposed in the casing beneath the brake drumand comprises essentially a pair of levers of the first order havingtheir fulcrums on the casing and being connected for movement in unisonin opposite senses, the outer ends of the levers being connected bylinks to the lugs I I, Ha and H! on the secondary bands. Considering theleft-hand side of the casing in Figure 1 (in conjunction with Fig. 2),spaced supports l3 and I4 secured to the bottom of the casing Iconstitute fulcrums for a pair of oppositely disposed levers I5 and I6.Each lever comprises a pair of similar plates riveted or welded togetherin spaced relation, the plates is disposed within a lying one on eitherside of the fulcrum support [3, M. Similar spaced fulcrum supports aredisposed symmetrically on the right-hand side of the casing, one ofwhich is shown at I8 carrying a lever H9. The inner ends of the leversl6 and it are recessed to receive a pin 2%. It will be understood thatthere is a similar lever behind lever I9 which is similarly mounted on afulcrum support behind lever [B and is similarly interconnected with thelever l behind lever 16'.

A reaction link 2! is pivoted at 22 to the outer end of lever 16 andcarries at its upper end a pin 23 which engages within the hook slotformed' in the lug Ha which as previously described is mounted on thefree or reaction end of the secondary brake band 6. The reactionlink 2lis of bell-crank form having an arm 24 which is curved and cut away asshown in Figure 1 to clear the fulcrum M. d

The extremity of the arm 24 is formed with an enlargement 25 having anaperture or slot and lying within the space between the two plates whichconstitute the lever I6. Within the eye or slot is located a slipfriction device 26 consisting of a short length of helical spring whichis compressed within the side plates aforesaid. I The lever I? (see Fig.2) is similarly pivoted at 22a to areaction lim 2! carrying at its upperend a pin 28 which engages in-the hook slot of the second lug ll securedto the reaction end of the secondary brake band 5.

The balancing lever i9, which as previously described is interconnectedwith balancing lever I6, is connected to the lug 62 on the secondarybrake band 6 by a balancing link 29 pivoted to the lever at 30 andhaving a bell crank arm 3! with an apertured enlargement 32accommodating a slip friction device 3 3, the arrangement bein generallysimilar to that of the reaction mm; 2!. It will be understood that thereis a second balancing lever, similar to lever H), which isinterconnected with balancing lever l5, and this second lever isconnected to the secondary brake band 5 by abalancing link and lug whichare similar in all respects to the link 29 and lug i2 just described. Hv

Applicati'n of the braking force is effected by any convenient meanssuch as a hydraulic or pneumatic cylinder (not shown) acting upon apiston rod 3 pivoted at 35 to a link 36 composed o fparallel spacedplates, which link is pivotally connected by means of a pin 37 to thereaction links 2! and 12'! and by means of a pin 38 to the tie link 39which is curved in elevation and carries at its upper end a pin 40 whichengages n the hook lugs 1 attached to the end of the primary brake band4. v Means are provided for guiding the upper parts of thebrake bandsintheir limited circumferehtial motions, and comprise a pair of plates4! and 4? located in spaced relationship with regard to the verticaldiam'etric plane ofthe drum. Each plate extends laterally across thethree bands as shown in Figure 3, the plate l! having an outwardlyprojecting rib 43 guided between a pair of fins 44 extending inwardlyfrom the cover 3 of the brake casing. Theplate M is riveted to the outerbrake bands 5 and 6 and is provided with a recess 45 which receives theinner or primary band 4. The plate 42 is similarly arranged andconstructed. Plates 46 and ll connecting the secondary brake bandsan'daffording a guide for the primary band are preferably provided inthe lower part of the brake casing. These plates are similar to theplate 4'! and serve also to take the weight of the primary band when thebrake is in the off position.

The duty of supporting the weight of the brake bands collectively whenno braking force is being applied comes on the reaction and balancinglinks, e. g. links 2! and 29. It will be appreciated from aconsideration of Figure 1 ofthe drawing that when the lower part of thebrake band as a whole has dropped to the requisite clearance from thedrum' surface, the inner arms of the equalizing levers it and I9 willhave risen by such an amount that the slip friction members 26 and 33will have reached the top of the apertures in the reaction and balancinglinks. As no further movement of the levers can take place withoutdisplacement of the friction grips, the weight of the bands is thusadequately supported. The diameter of the apertures which embrace thefriction devices is chosen so that the amount which the lower part ofthe band can drop when the brake is released is such as to produceapproximately an equal clearance between the top portion of the band andthe drum. It will of course be understood that although the frictionafforded by the devices in question is adequate to support the weight ofthe brake bands, it will not be sufficient to resist displacement in theopposite direction when the brake lining wears, and the brakeapplication force draws the band closer to the drum. The frictiondevices are self-adjustin'g and will accordingly become progressivelydisplaced upwardly relative to the levers as the brake lining wears,thus maintaining a constant clearance relative to the drum when thebrake is released irrespective of wear.

Upon application of the braking force through the piston rod 3G, thelink to is rotated in a counterclockwise direction about the pivot 3"!and the tie link 39 is pulled down, thus transmitting a pull to theapplication end of the primary brake band 4. This tends to cause aconsequen tial displacement in the same direction to the reaction end ofthe primary band, but as this end is coupled to the application ends ofthe secondary bands 5 and 6, the braking force is transmitted to thesaid application ends of the secondary bands.

While the piston rod is causing a pull on the tie link 39; the reactionlinks (e. g. 2 l) thrust upwardly against the lugs ll, lid on thesecondary brake bands. In this operation the friction devices 25 and 33are displaced upwardly (as Wear occurs) on their levers after the playpermitted by the apertures has been taken up. Through the action of theequalizing levers the corresponding balancing links (e. g. 29) supportand thrust upon the secondary brake bands on the opposite side of thedrum, thereby relieving the drum of one sided load by affording abalancing moment on that side of the drum opposite that on which thebrake applying force acts. Upon relief of the braking pressure, thestresses are released and the bands are released from the drum, thereaction and balancing links being stabilized by the engagement of the-opposite ends of the apertures in the crank arms of the linkssurrounding the friction devices. The stresses imposed on the bands bytheir contraction upon the brake drum will normally be adequate toexpand the hands when the pressure is relaxed. If desired, however, anauxiliary spring or springs may be provided between the bande'xtremitiesfor the purpose of opening the when the application force is released.

It is to be understood that for conditions of balance, the line ofaction of the piston rod 34 should pass approximately through the pivotconnections (e. g. 22) between the reaction links and the equalizinglevers and also through the fulcrum of the equalizing lever. In additionthe line of pull of the tie link 39 should pass through or adjacent tothe connection 23.

Whilst in the example previously given there is a single primary band incombination with two secondary bands, combinations of more than threebands are readily provided by coupling the reaction ends of one or bothof the secondary bands to the application end or ends of an additionalband or bands in a similar manner to that in which the reaction end ofthe primary band is coupled to the application ends of the secondarybands, while the reaction ends of the ad ditional bands have reactionlinks and balancing links coupled by equalizing levers after the mannerof the previous example. Thus the braking may be transmitted in seriesfrom band to band.

We claim:

1. A band brake comprising a brake drum, brake band means including atleast a primar gapped band and two secondary gapped bands disposed sideby side around said drum, means for applying the brake operating forceto one end of the primary band with the reaction end thereof coupled tothe application ends of the secondary bands, equalizing lever meansconnected to the reaction ends of the secondary bands for transmittingthe reaction equally and in the same sense to said secondary bands atthe opposite side of a diametric plane of the brake drum in such amanner that the moments of the forces acting about the drum axis on theapplication of the brake are substantially balanced, and slip-frictionmeans included in the connections between the secondary bands and theirequalizing lever means arranged so that when the bands are in the oifposition they are supported with a substantially constant clearanceirrespective of wear.

2. A band brake comprising a brake drum, brake band means including atleast a primary gapped band and two secondary gapped bands disposed sideby side around said drum, means for applying the brake operating forceto one end of the primary band with the reaction end thereof coupled tothe application ends of the secondary bands, oppositely disposedequalizing levers, fixed fulcrums for said levers, links connecting theouter ends of said equalizing levers to points on the secondary bandssymmetrically disposed on opposite sides of the diametric plane of thedrum for transmitting the reaction equally and in the same sense to saidsecondary bands so that the moments of the forces acting about the drumaxis on the application of the brake are substantially balanced, andslip-friction connections between said links and equalizing leverswhereby the bands in the oil position are supported with a substantiallyconstant clearance irrespective of wear.

3. A band brake according to claim 2, wherein the said slip frictionalconnection comprises a lost motion means such that when the brakingforce is relieved the bands leave the drum and are supported by thelinks against the frictional connection.

4. A band brake according to claim 3, wherein the said links have leverarms the ends of which have a combined frictional and lost motionconnection with the equalizing levers.

5. A brake band according to claim 4, wherein the said equalizing leverscomprise spaced plates between which are located the slip-frictiondevices having a lost motion connection with arms on the links.

6. A band brake according to claim 2, wherein the force application endof the primary band is connected by a tie link to a pivoted lever whichis located on the same side of a diametric plane of the brake drum asthat on which the reaction link is situated and to which the brakingforce is applied.

7. A band brake according to claim 6, wherein the line of application ofthe force is arranged to pass through or adjacent the fulcrum of theequalizing lever connected to the reaction ends of the secondary bandsand also through or adjacent the connection of the reaction link withthe said lever.

8. A band brake according to claim '7, wherein the line of pull on theprimary band passes through or adjacent the connection between thereaction ends of the secondary bands and the reaction link.

A. GORDON WILSON. A. A. MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,005,284 Wilson June 18, 19352,066,308 Pomeroy et a1. Dec. 29, 1936 2,302,521 Bjorge Nov. 17, 1942

